1. Field of the Invention
The present invention relates to a water-decomposable absorbent article for pantiliners, sanitary napkins, incontinence pads, diapers, and the like.
2. Description of the Related Art
Recently, absorbent articles disposable in flush toilets have come available, including, for example, pantiliners, sanitary napkins, incontinence pads, diapers, etc. For example, Japanese Unexamined Patent Publication (Kokai) Nos. Heisei 8-38547 and 8-19571 disclose water-decomposable absorbent articles comprising a water-decomposable absorbent layer and water-decomposable surface and back layers between which the absorbent layer is sandwiched.
As having such a water-decomposable back layer, these water-decomposable absorbent articles have a problem in that the excretions having been absorbed by the absorbent layer therein may lower the strength of the back layer that have received them, and may pass outside through the back layer.
To solve the problem, the water-decomposable back layer is covered with a water-insoluble (water-impervious) film to thereby prevent the liquid leakage through it; or a water-repellent sheet is used for the back layer. However, such a water-insoluble film or water-repellent sheet greatly lowers the decomposability in water of absorbent articles having it.
Japanese Unexamined Patent Publication (Kokai) No. Heisei 6-101154 discloses an absorbent article, in which the back layer of a water-decomposable material is covered with a water-soluble polymer film of polyvinyl alcohol (PVA) and an absorbent layer is provided on the polymer film. In the absorbent article disclosed in this publication, the PVA film is to prevent the leakage of excretions to the back layer. In this, however, the PVA film underlies the absorbent layer, and the PVA film and the absorbent layer are separated. Therefore, the excretions having passed through the absorbent layer will concentrate locally in the PVA film and will dissolve the local area of the PVA film in which they have concentrated. As a result, the PVA film will be locally holed or broken, and could not ensure satisfactory leakage prevention.
On the other hand, the absorbent layer may be thickened so that it can absorb the majority of excretions to thereby prevent the back layer from being kept in contact with a large amount of liquid. However, such a thick absorbent layer is unfavorable since the absorbent articles having it could not be soft and will have a hard feel.
An object of the invention is to provide a water-decomposable absorbent article which can surely prevent a liquid leakage through it, without having a hard feel, and can well decompose in water.
According to one aspect of the invention, a water-decomposable absorbent article may comprise a water-decomposable back layer, a water-decomposable and liquid-pervious surface layer, and a water-decomposable absorbent layer sandwiched between the back layer and the surface layer, wherein;
the absorbent layer is formed of at least one composite sheet of a water-soluble or water-swellable polymer layer and a water-decomposable fibrous layer, of which the uppermost layer adjacent to the surface layer is the water-decomposable fibrous layer.
For the absorbent layer of the absorbent article according to the invention, a fibrous layer is integrated with a water-soluble or water-swellable polymer layer to form a composite sheet. The excretions having been absorbed by the absorbent article reach the fibrous layer and diffuse therein, and then move to the polymer layer that is two-dimensionally integrated with the fibrous layer. Accordingly, in the absorbent article, the excretions do not locally concentrate in the water-soluble or water-swellable polymer layer. In this, therefore, the fibrous layer does not peel from the polymer layer, and the polymer layer is not holed or broken. As a result, the polymer layer that constitutes the absorbent layer surely acts to prevent the excretions from leaking out to the back layer. Since the polymer is soluble or swellable in water, the polymer layer easily decomposes in water when the absorbent article is disposed of in water.
The fibrous layer in the absorbent article of the invention may be made of tissue (water-decomposable paper), air-laid pulp, water-decomposable non-woven fabric or the like.
The absorbent layer in the absorbent article may be formed of two or more composite sheets stacked to each other, in each of which the water-decomposable fibrous layer is located to face the side of the surface layer.
The absorbent layer may be formed of one of the composite sheet which is folded into two so that constituent layers thereof are in an order of water-decomposable fibrous layer, polymer layer, polymer layer and water-decomposable fibrous layer with the uppermost water-decomposable fibrous layer being adjacent to the surface layer.
As set forth above, the embodiment of the absorbent article where the fibrous layers of tissue (water-decomposable paper) or the like are alternately laminated with the polymer layers is advantageous in that the excretions having been absorbed by it are more surely prevented from leaking out through the back layer. This is because, even when one of the polymer layers adjacent to the surface layer is decomposed by the excretions, the other fibrous layers and polymer layers underlying it can still ensure leakage prevention.
The water-soluble or water-swellable polymer layer may be, for example, a polyvinyl alcohol layer, and a basis weight (a basis weight is also referred to as Metsuke) of the polyvinyl alcohol layer is preferably at least 10 g/m2. The polyvinyl alcohol layer may be in the form of a film, and it may be laminated and integrated with the fibrous layer. On the other hand, the polyvinyl alcohol layer may be formed on the fibrous layer by coating polyvinyl alcohol thereon, and this may be integrated with the fibrous layer.
If desired, an additional absorbent layer of pulp, tissue (water-decomposable paper) or the like may be provided between the composite sheet and the surface layer of the absorbent article of the invention.
According to another aspect of the invention, a water-decomposable absorbent article may comprise a water-decomposable back layer, a water-decomposable and liquid-pervious surface layer, and a water-decomposable absorbent layer sandwiched between the back layer and the surface layer, wherein;
the absorbent layer includes two water-decomposable fibrous layers and a water-soluble or water-swellable polymer layer sandwiched between the water-decomposable fibrous layers.
In this aspect of the invention, the absorbent layer comprises two fibrous layers of tissue, water-decomposable non-woven fabric, air-laid pulp or the like, and a polymer layer of PVA or the like sandwiched between the fibrous layers. The excretions having been absorbed by the absorbent article of this case first reach one fibrous layer adjacent to the surface layer, and then move to the polymer layer that underlies the fibrous layer. Therefore, they are prevented from penetrating into the back layer. In the absorbent article of this case, even when the polymer layer is dissolved by the excretions and the excretions thus having dissolved the polymer layer reach the other fibrous layer that underlies the polymer layer, they can be well absorbed by the underlying fibrous layer and are prevented from leaking out through the back layer.
The polymer layer in the absorbent article of this case may be formed on at least one fibrous layer by coating a polymer thereon; or a polymer film may be laminated on at least one fibrous layer to form the polymer layer thereon. As the case may be, a polymer film of PVA or the like may be simply sandwiched between two fibrous layer, without being bonded thereto.